“Pan & scan” (pan) is a term typically referred to cropping off horizontal sides of an original widescreen image having, for example, an aspect ratio of 2.35:1. Typically, pan may be used for fitting the most significant portion of the picture for display on, for example, a 16:9 aspect ratio display screen. The analogous cropping off in the vertical direction is typically referred to as “tilt & scan” (tilt). Zoom function may be used for better recognizing details. The zoom function may also be chosen for adapting pictures with different display ratio on the given screen from letterbox to different zoom modes. Different combinations of zoom, scan and tilt functions may be selected and controllable by a viewer using, for example, a conventional hand held remote-control unit.
FIG. 1a illustrates a picture 100 displayed on a display screen 106 without cropping and in a non-zoomed mode. In FIG. 1b, a zoom function is applied to picture 100 such that only a picture portion 105a of picture 100 is displayed on display screen 106. In FIG. 1b, portion 105a or picture 100 is zoomed center by having a center point 110 of display screen 106 at the same point as a center point 110′ of picture 100. The zoom function results in a portion 105b of picture 100 being invisible for being outside the viewing area of screen 106. FIG. 1c illustrates picture portion 105a, displayed on display screen 106 that results from applying a combination of both a zoom function and a pan function. As a result, center points 110 and 110′ do not coincide. Similar symbols and numerals in FIGS. 1a, 1b and 1c indicate similar items or functions.
When a viewer is watching a movie on display screen 106 of FIG. 1b, a particular object, not shown, may catch the viewer's attention. Such object may move in relation to screen 106 in a particular direction, for example, to the right of FIG. 1b. Consequently, the viewer might tend to follow the moving object by changing the viewer's head direction and/or the direction to which the viewer's eyes are directed to the right of FIG. 1b. 
It may be desirable to employ a dynamically tracking pan function, a dynamically tracking tilt function or a combination thereof (each being referred herein as dynamically tracking pan/tilt function) responsive to the viewer head/eye movement. Such function may be used in order to maintain the moving object within visible portion 105a instead of being invisible.
In carrying out an inventive feature, as long as the viewer's viewing direction is directed toward a center region of a display screen, dynamically tracking pan/tilt function is not performed or is disabled. Once the viewer's viewing angle crosses a first threshold angular direction, away from the screen center and towards, for example, a right side border of the screen, dynamically tracking pan function is enabled so as to shift the displayed picture in the opposite direction. The result is that the aforementioned moving object is shifted closer to the center of the screen. Advantageously, that portion of the zoomed picture that has been heretofore invisible will, consequently, shift into the viewing area of the display screen. Therefore, the moving object will, advantageously, tend to remain closer to the screen center.
Assume that, after the pan function is initiated, the viewer's viewing angular direction begins changing in the opposite direction. This may result, for example, because the moving object has shifted by the aforementioned picture shift operation of the pan function. It may be desirable to avoid a picture bounce in the vicinity of the first threshold angular direction.
In carrying out a further inventive feature, the viewer's viewing angular direction is required to cross a threshold angular direction that is smaller than the first threshold angular direction in order to suspend or stop further pan function operation. Thereby, advantageously, a hysteresis feature is incorporated into the pan/tilt function.
In carrying out another inventive feature, when the viewer's viewing angular direction crosses an even larger, second threshold angular direction away from screen center and towards the same side border of the screen, the picture will pan at a faster rate than when the viewer's viewing angular direction is between the first and second threshold angular directions. The faster rate is applied, advantageously, to prevent the moving object from disappearing from the visible portion of the screen.
The hysteresis feature can also be incorporated with respect to crossing the second threshold angular direction. Similarly, incorporating multiple thresholds and corresponding hysteresis features are also possible.
Assume that, after the picture shifting has stopped, the viewer turns the head in an opposite direction to that previously triggering the pan function. When the viewer's viewing angular direction exceeds a third threshold angular direction, pan function in the opposite direction is initiated.
In carrying out an even additional inventive feature, the third threshold angular direction is adaptably determined by the extent of the accumulation of the picture shifting present at the time the picture shifting stopped. Advantageously, a hysteresis feature may also be incorporated with respect to crossing the third threshold angular direction.
A sudden fast rate of change of the eye movement, head-tracking or face orientation of the viewer might indicate a disturbance unrelated to the displayed picture. Therefore, in carrying out a further inventive feature, detection of such fast rate of change will have no effect on the pan/tilt function.
It may be desirable to complement the zoom or dynamically tracking pan/tilt function by making the perceived sources of sound such as speakers dynamically follow the dynamically tracking pan/tilt function. Advantageously, this is accomplished by adaptively mixing, for example, two stereo channels in response to control signals that control the pan/tilt function. Thus, as the displayed image shifts by the dynamically tracking pan/tilt function, the locations from which the sound is perceived to originate also track the display image to which the zoom or tracking pan/tilt function is applied. In short, the stereophonic width dynamically varies in accordance with the stereoscopic width.
An article entitled, THE SIMULATION OF MOVING SOUND SOURCES by John M. Chowning, (J. Audio Eng. Soc. 19, 2-6, 1971) describes an arrangement in which an illusory sound source can be moved through an illusory acoustical space. A number of independent audio channels is transformed into two or four channels where the location static or dynamic of each input channel can be independently controlled in an illusory environment. The method controls the distribution and amplitude of direct and reverberant signals between the loudspeakers.
U.S. Pat. No. 5,046,097, Lowe, et al., describes a process to produce the illusion of distinct sound sources distributed throughout the three-dimensional space containing the listener, using conventional stereo playback equipment.
U.S. Pat. No. 5,742,687 shows an embodiment for an audio-visual reproduction system in the form of, for example, a television set. In the case where a stereo audio signal is supplied, the position of the sound source that reproduces the left channel will present a virtual shift to the left. Similarly, the source representing the right channel signal will undergo a virtual shift to the right.
U.S. Pat. No. 4,219,696, Takuyo Kogure et al., discloses mathematics which would allow placement of sound image anywhere in the plane containing the two loudspeakers and the listener's head, using modified stereo replay equipment with two or four loudspeakers. The system relies on accurate characterization, matching, and electrical compensation of the complex acoustic frequency response between the signal driving the loudspeaker and the sound pressure at each ear of the listener
U.S. Pat. No. 4,524,451, Koji Watanabe, explains a basis for the creation of “phantom sound sources” lateral to or behind the listener.
U.S. Pat. No. 5,987,141, Hoover, teaches a stereo expander in which stereophonic audio processing system having left and right stereophonic sound channels with respective loudspeakers therefor is presented. The system is provided with spatial expansion of the stereophonic sound so that a first pair of spaced-apart loudspeakers will acoustically appear to be spaced further apart than they actually are.